Remote indicator for radio pulse systems



Sept. 2, 1947. G, E. WHITE REMOTE INDICATOR FOR RADIO PULSE SYSTEMSFiled May 25, 1943 lNvENToR.

GIF-FO E-WHITE` HIS ATTORNEY Patented Sept. 2, 1947 REMOTE INDICATOR FORRADIO PULSE SYSTEMS Gifford E. White, Hempstead, N. Y., assignor toSperry Gyroscope Company, Inc., a corporation of New York ApplicationMay 25, 1943, Serial No. 488,369

9 Claims.

This invention relates, generally, to pulse systems, such as those usedfor indicating and measuring distance between two objects.

The invention particularly concerns a remote indicator circuit which maybe used in connection with receivers providing a high resolution ofreceived pulses of energy.

Radio pulse systems have 4been used extensively for measuring distanceand many different systems have been proposed. In some systems a shortsharp .pulse of high frequency energy is transmitted and the timeinterval for this pulse to be reflected by an object and received at thepoint from which it is usually transmitted, is measured. Since the timeinterval involved is relatively short, the most advantageous method ofindication is that provided by a cathode ray tube.

The electron beam of a, cathode ray tube may be swept across the screenat a frequency having an integral relation with the repetition rate oftransmitted pulses. Received pulses are applied to the intensity controlgrid of the cathode ray tube causing a spot to appear when a pulse ofenergy is received. By suitably synchronizing the sweep of the cathoderay beam and the transmission of pulses, it is possible to provide anindication of the elapsed time between the transmission of pulses andthe reception of reflected pulses.

It will be apparent that the accuracy of such an indication depends uponthe velocity of the sweep of the cathode ray beam, and also upon thequality ofv resolution provided by the receiver in applying pulses tothe intensity control grid of the tube. It is necessary in most cases touse high iidelity receivers using a wide band amplier for applying ashort, sharp pulse to the intensity control grid of the cathode ray tubethat has approximately the same Wave shape as a transmitted pulse.

In addition to range indicators, such as that described, the same radiopulse systems may also be used for indicating the approximate locationof an object. This may be accomplished by periodically scanning adirectional antenna for the transmitter or receiver over a portion ofspace, and scanning the beam of a cathode ray tube in synchronism withthe antenna. The application of a received pulse of energy to theintensity control grid of the cathode ray tube causes a spot to appearVupon the screen of the tube. 'I'his spot is located on the tube in a,position corresponding to the position of the antenna at the time thepulse is received, thus indicating (Cl. Z50- 1.62)

2 the approximate direction from which the pulse is reflected orradiated by an object. In this type of indication the cathode ray beamis moved at a slower rate over the screen of the tube, reducing thenecessity for providing high resolution of received pulses.

It is dicult to supply short, sharp pulses to a remote indicator orcathode ray tube because such pulses include a very wide band offrequencies. The sharp or square Wave shape of such pulses is obtainedby IJIOVdng a relatively large number of harmonics, in addition to thefundamental frequency. It is necessary to transmit all of theseharmonics, and particularly the upper harmonics, in order to maintainthe square Wave shape.

Since the upper harmonics have relatively high frequencies, it is dicultto transmit them over great distances, even with high impedance coaxialcables. 'I'he best of such cables have a certain amount of capacity.This capacity is proportional to the length of the cable. Intransmitting short pulses over such cables, it is necessary to chargethe capacity of the cable during a very short interval. The currentnecessary to charge the capacity Within this short time is beyond thecapacity of the ordinary electronic tubes which are customarily used inpresent day equipment. Even if special tubes are used to provide thenecessary charging current, a pulse loses its sharpness duringtransmission because the higher harmonics are by-passed to ground.Hence, the high resolution provided by the receiver may only be used ifthe indicator is located near the receiver.

However, the same high fidelity receiver may also be used to controlremote indicators which do not require high resolution of receivedpulses. Such indicators may be actuated by a pulse that has a large timeinterval and a smooth wave form as compared with short, sharp receivedpulses. It is only necessary that the pulse applied to a remoteindicator have suicient amplitude to actuate the intensity control gridof the cathode ray tube.

It is, therefore, one object of the present invention to provide aremote indicator circuit that may be used with a high resolution pulsedetection system,

Another object of the invention is to provide a remote indicator circuitin which sharp received pulses are converted into a form which is moreeasily transmitted to a remote point.

Other objects and advantages of the invention will become apparent fromthe following specification and accompanying drawing.

The drawing, which contains only one gure, shows a radio pulse system,such as that heretofore described, including a remote indicator circuitcomprising the present invention.

As shown-in the drawing, an antennal having a reflector 2 for providingthe antenna with a highly directional beam pattern is supported on ascanner, indicated generally at 3. The scanner 3 includes a main portion4 forming the housing. of a motor which is adapted to rotate a bracket 5about a spin axis E of the scanner. The bracket 5 has arms 'I and 8 inwhich is journalled a shaft 9 that carries the antenna I and reector 2.A motor I I, mounted on the bracket 5, drives through a crank wheel I2,link I3, and an arm I4 on shaft 9, to slowly oscillate shaft 9 about anod axis I'I.

The antenna I is connected by suitable wave guides I8, I9, 2I and 22having conventional rotary joints, to a high frequency radio receiver23. The receiver 23 may be of any suitable design including a: wide bandamplifier for maintaining the wave form of short, sharp pulses Which-maybe received.

Pulse energy may be radiated by a transmitter 36' (not shown) located atthe receiver or by a transmitter at the object, the distance of which isto be measured. Such transmitters are usually designed to periodicallyradiate short, sharp pulses of ultra high frequency radio energy. It isnecessary that the receiver 23 be of a high delity type providing auniform response of a very wider band of frequencies depending upon thetime interval of the pulse being received. Such receivers and amplifiersare sometimes referred to as video circuits.

The output of receiver 23 is connected by coaXial Ycable 25 to intensitycontrol grid 23y of cathode ray tube 2 1. The tube 2 is normally biasedto cut-off. The reception of a pulse by the receiver-23 ,causes apositive voltage pulse to be applied to the grid 26, thereby permittingthe electron beam to iiow for a short time interval as l."

determined by the pulse.

The manner in which the elect-ron beam is positioned on the screen 28 ofthe tube 2'! will'now be described. A synchronizer 3I isY adapted tosynchronize the receiver 23 and a range sweep generator 33- withthe'transmitterof the short, sharp pulses which are to be received. Thesynchronizer V3| may be controlled directly by the transmitter if it islocated near the receiver or in the case of a remote transmiter, by aseparatesynchronizing channel. The synchronizing circuit may be ofA anyconventional design, the specific details of which do not form a part ofthe present invention.

The synchronizer 3| vmay be used to control a gate circuit in thereceiver 23 to determine the period during which the receiver issensitive as well as to control a range sweep generator 33.

Immediately following the transmission of each pulse, synchronizer 3l'causes the range sweep generator 33 to apply aV voltage to verticaldeilecting plates 35 and 36 of the cathode ray tube 2l to sweep thecathode ray beam across the screen 23.Y The velocity of this sweep mustbe sufiiciently high to completely move the beam across the screenwithin a time interval during which it is contemplated a pulse willk bereceived. This time'interval is usually of the order of a fewmicro-secondsg depending upon the distance being measured.

The horizontal position of the electron beam, as determined byhorizontal deflecting plates 39 and 4I, may be adjusted in accordancewith the nod angle of the antenna, as described in copending applicationSerial No. 483,698, filed April 19, 1943, for Indicating method andapparatus for adetection system, in thename' of J. E. Shepherd. Asuitable rotary transformer 43 of any conventional type is energizedfrom a source M. through slip rings 40. The windings of the transformerare displaced in accordance with movements of the antenna I about thenod axis. The amplitude of the output voltage of the transformer therebyvaries inaccordance with the nod position of the antenna I. This voltageis supplied through slip rings 5l) and leads 45 and i6 to a suitabledetector and amplifying circuit' li?, which may be of conventionaldesign. such as that shown in the above-mentioned copending applicationwhich will apply a voltage to the horizontal rdeflecting plates 39 and4I to position the cathode ray beam on the screen 23 in accordance withthe nod position of the antenna I.

The foregoing description isA one example of many systems which havebeen proposed to indicate the distance between two'objects by measuringthe time of travel Aof a pulse of high frequency energy. The system,shown in the drawing, also provides an indication of the path throughwhich the directional beam pattern of the antenna I is being moved atthe instant a pulse of energy is received. As has been explained, it isnecessary that the cathode ray tube 21 be located reasonably near thereceiver 23. It is diicult to transmit a short, sharp pulsecorresponding to the received pulse over an appreciable distance eventhough a high impedance coaxial cable, such as cable 25, is used. Sincethe range sweep generator Ysweeps the cathode ray beam vertically acrossthe screen 28 within the space of a few micro-seconds, it is, ofcourse,necessary that a short, sharp-pulse be applied to the grid-2B in orderto provide reasonable resolution on the screen 28'.

In -addition to the cathode ray tube 21,. it is sometimes desirable tohave an indicator of some form at a point remote from the receiver 23.For example, in the case of object detection equipment, it may bedesirable to have `a local indicator, such as the tube 21, at the pointat which the receiver 23-is located, and to have a remotely positionedindicator for use of a coordinating oiiicial; In such a case, a numberof receivers scattered over a large area may have remotely controlledindicators located at a central point so the activitiesV of the variousreceivers can be coordinated.

Another application is that of air-borne equipment in which one highYresolution indicator is provided near the receiver 23 and Vremoteindicators are provided'for -a pilot and, in some cases, for a gunner ina turret-which is mounted on an aircraftJ for rotation about twoindependent axes. The diiiicultiesof suppl-ying a sharp, short pulse tosuch` remote pointsare obvious. difficulty is that v.encountered inconnecting a coaxialcable or other high impedanceY transmission line toa, turret of the character described-'because rotary coupling rand otherbulky; and expensive equipment is required. Even if a'suitabletransmission line were provided', the; tsharpness of the` pulsev wouldbe lost in transmission due tothe capacityinherentgin such a cable. V

" As has been heretofore mentioned, thec'apacity One majorV of such atransmission line increases with its length. As this capacity increases,the current drain on an amplifying tube also increases. The pulses areof extremely short duration, so it is necessary to charge the capacityof the line within a relatively short time. Hence, the charging currentmust be high and may exceed the capacity of tubes usually used in thistype of equipment. If the pulse is amplified suiiiciently to overcomethe loss in amplitude during transmission to a remote indicator, theamplifier is called upon to provide an even higher charging current.However, it is y'possible to take advantage of the fact that a remoteindicator need not be supplied with a short, sharp pulse in order toindicate the position of the receiving antenna at the instant a pulse isreceived.

One arrangement for scanning the electron beam of a remote indicator isshown in the drawing. A remotely positioned cathode ray tube 5| has itscathode ray beam deflected by horizontal deiiecting plates 52 and 53 andvertical deiiecting plates 54 and 55, respectively. Suitable voltagesare applied to these plates in a manner to be described which causes theelectron beam to scan the screen 56 of the tube 5| in synchronism withthe scanning movements of the antenna l.

As has been described, the voltage output of the rotary transformer 43varies in amplitude in accordance with the nod angle of the antenna Thislvarying voltage is connected by leads 58 and 59 to a winding of arotary transformer 6|, the rotor of which is rotated in accordance withthe spinning movements of the scanner 3. The transformer 6| includestwo-phase windings each leg of which has an end connected to ground, asat 62. The free end of the two-phase windings are connected to leads 63and 64. It will be apparent that voltages appearing on leads 63 and 64are displaced electrically by approximately 90.

Rotation of the antenna about the spin axis 6 of the scanner causesrelative movement between the windings of transformer 6| which variesthe voltage appearing on leads 63 and 64 at a spin frequency dependingupon the spinning rotation rate of the scanner. Thus voltage having afrequency corresponding to the spin frequency and varying in amplitudein accordance with the nodding movements of the antenna appear on leads63 and 64. These voltages, which are displaced in phase in 90 aresupplied to suitable detector and amplifier circuits 65, and 66.

A similar voltage appears on lead 68. The voltage appearing on lead 61is applied to horizontal defiecting plates 52 and 53, whereas thevoltage appearing on lead 68 is applied to vertical deiiecting plates 54and 55 of the tube 5|.

Since these two voltages are displaced by 90, it will be apparent thatthe cathode ray beam of the tube 5| is rotated at the spin frequency todefine a circle on the screen 56. However, the amplitude of thesevoltages is varied in accordance with the nod angle of the antennaHence, the diameter of the circle defined by the cathode ray beamvaries, and causes the beam to follow a spiral pattern in scanning thescreen 56.

It will be apparent that the beam of the cathode ray tube 5| iscontinuously positioned in accordance with the position of the antenna lon the scanner 3. Therefore, a spot appearing on the screencorresponding to the reception of a pulse by the receiver 23 will bepositioned in accordance with the position of the antenna-I at theinstant the pulse is received.

11n order to transmit a received pulse to the remotely positionedcathode ray tube 5|, the sharp pulse is first averaged by a network,such as the lter network 1| including a resistor 12 and condenser 13. Byappropriately selecting the resistance of resistor 12 and capacity ofcondenser 13, the sharp, short pulse may be converted or averaged to apulse of any desired amplitude and duration, In this manner, the shortpulse may be spread over -a greater time interval due to the chargingand discharging action of the condenser 13. Obviously, the higherfrequencies are bypassed by the condenser, thus reducing the amplitudeof the pulse. However, the increased time interval makes it possible toamplify the pulse in such a manner that it may be transmitted over aconventional transmission line.

The averaged pulse is now'applied by lead 15 to the grid of aconventional triode amplifier 1'6, the bias of which is provided by aresistor 11 in the circuit of cathode 18. Suitable voltage is appliedfrom a source 19 through a load resistor 8| to plate 82 of the tube 16.The ampliiied pulse appearing across resistor 8| is coupled by condenserto any transmission line 83, which may be of either a low impedance orhigh impedance type. Since the pulse no longer contains the higherharmonics, it is not essential that a high impedance transmission linebe used. The transmission line 83 is connected to grid 85 of the cathoderay tube 5|. f

When a short, sharp pulse is received by the antenna I, the receiver 23applies a similar short, sharp pulse to the grid 26 of the local cathoderay tube 21, thereby providing a high resolution range indication on thescreen 28. At the same time, the receiver output, as represented by lead15, is applied to the averaging or filter network 1|, whereby the timeinterval of the pulse is enlarged and its amplitude and sharpnessreduced. The pulse to be averaged is amplified by the amplifier 16 andsupplied to grid 85 of the cathode ray tube 5|. Since the beam of thetube 5I is scanned in accordance with the scanning movements of thescanner 3, a pulse on the grid 85 causes a spot to appear on the screen56 of the tube 5| and the spot is positioned to indicate the directionfrom which the pulse is received.

If a low impedance transmission line were connected directly from thereceiver 23 to the grid 85, the amplitude of the received pulse might bereduced to such a point that it would be insuiiicient to actuate thegrid 85. This situation cannot be overcome by merely amplifying thesharp pulse because, as has been explained, a high current is necessaryfor even a high impedance coaxial transmission line of appreciablelength due to the shortness of the pulse and the shortness of thecharging interval. By first averaging the short, sharp pulse and thenamplifying it, it is possible to use a high capacity line to apply thepulse to grid 85 of the remote indicator.

It will be apparent, therefore, that the present invention permits theuse of the output of a wide band amplifier to energize the grid of aremote indicator of a cathode ray tube by first averaging the output andthen amplifying it before supplying the pulse to the connecting linebetween the grid of the remote indicator and the ampliier. Thelengthened pulse permits a longer charging interval so the current drainon the amplifier is reduced, to a point where conventional tubes may beused. Furthermore, the higher harmonics of the sharp pulse are dis-.turret on an aircraft,

ascesa-i -carded so thenecessity fora high impedance transmissionlineis'reduced. AFor rthese reasons, signals maybe readily supplied to aremote indicator, even though it is positioned within a However, this is`merely s intended as one illustration of the use ,of the presentinvention. ObviouslyVitihas other uses vof equal importance.

Since many changes could be made in the above construction and manyapparently widely .different embodiments of kthis invention could bemade without departing from the scope thereof, it is intended thatkallmatter contained in the above description or shown in theaccompanying ing drawingsshall be interpreted as Aillustrative and not,in a limiting sense.

What is claimed is:

1. In a radio pulse Yreceiving system, in wcornblnation, a local cathoderay tube, a -wide band amplifier for providing a `high resolutionindication of lreceived pulses on the screen of said local cathoderaytube, a remote indicator circuit including a cathode ray tube remotefrom said amplifier, an averaging network connected yto the output ofthe wide ,band amplifier for pulses, an ainplifierin circuit with s aidnetwork for amplifying said averaged pulses, and means connected to saidamplifier v'for supplying said amplied pulses to said remote cathode raytube.

3. lIn a radio pulse receiving system, in combinationfa wide bandamplifier constructed and arranged to maintain a high resolution Vofreceived pulses, Aa remote cathode ray tube at a distance from saidamplifier, avlter circuit connected to a voltage output of said wide-band amplifier for averaging the voltage envelope ofV Vsaid highresolution pulses, and means connected to said filter for supplying saidaveraged voltage pulses to the control grid of said remote cathodeV raytube.

4. In a radio pulse receiving system, in combination, a local cathoderay tube, a wide band amplifier for yproviding a high resolutionindication of received pulses on the `screen of said local cathode rayVtube, a Yremote cathode -ray tube at a distance from said amplifier, afilter circuit connected to a voltage output of said wide band amplierfor averaging the voltage of saidpulses, a voltage amplifier in circuitwith said filter for amplifying said averaged voltage pulses, and meansconnected to said amplifier for supplying said amplified voltage pulsesto the control grid of said remote cathode ray tube.

5. A radio pulse -system `comprising a directional antenna, means forscanning said antenna over a portion of space, a wide band receiverconnected to said antenna for detecting short pulses vof 1energyabsorbed by said antenna, a local cathode ray tube actuated by saidreceiver Yin accordance `with lsaid detected pulses, a re- 7 `motecathode ray tube, and averaging means connected to said .receiver and incircuit `with saidgremote cathode ray tube for averagingand applyingsaidpulses of energy to the remote cathode ray tube.

6. .A radio pulse -system comprising a direc- -ltional antenna,means-for scanning said antenna vover a portionfof space, areceiverconnected to said antenna and having a wide band amplier to.provide a high resolution indication on the screen of a ylocal cathoderay tube, a remote cathoderay tube, means responsive to saidscanningmeans for positioning the cathode ray beam of said remotecathode ray tube in accordance withsthe positionof said antenna, andaveraging means connected to said receiver for control- Yling saidremote cathode ray tube in accordance with ythe reception of energy bysaid antenna.

'1. A radio pulse system comprising a directional antenna, means forscanning saidantenna overa portion of space, a receiver connected tosaidantenna and having a wide band ampliiier to provide a `highresolution indication on the screen of alocal cathode ray tub'e, aremote `cathv0de ray tube, means responsive 'to said scanning means forpositioning the cathode vray beam of `said remote cathoderay tube inaccordance with the position of said antenna, means connected tosaidreceiver for averaging short, sharp pulses of `energy receivedthereby, and vamplifying means in circuit with said averaging means forcontrolling said remote cathode raytube .in accordance with thereception of energy by said antenna.

,8. .A radio pulse system comprising a directional antenna, means forscanning said antenna over a" portion of space, a receiver connected tosaid antenna and having a wide band amplifier to Vprovide a highresolution ,indicationonthe screen of a vlocal cathode ray tube,

filter for amplifying andapplying said averaged energy to the grid of aremote ycathode ray tube, andmeans for positioning the cathode ray beamof said remote cathode ray tube in accordance with the position of saidantenna.

9. A radio pulse Vsystem comprising ta directional antenna, means forscanning said antenna over a portion of space, a receiver connected ,tosaid antennaand having Va wide band amplifier to provide a highresolution indication of received pulses on the screen of va localcathode ray tube, a filter connected to the output of said ampliiier foraveraging the received pulses, an amplifier for controlling the grid ofa remote cathode ray tube in accordance with said averaged pulses, landmeans responsive to said scanning means for positioning the cathoderaybeam of said remote cathode ray tube vin accordance with the positionof said antenna.

GIEFORD E.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

